High strength composite of resin, helically wound fibers and swirled continuous fibers and method of its formation

ABSTRACT

A fiber reinforced resin composite and its formation method is disclosed. The process comprises applying resin in a metered amount to fiber strands, winding the coated strands onto a drum while simultaneously applying swirled continuous fibers to the area immediately to be covered by the strands as they are wound. The preferred material for both the wound strands and the swirled strand is fiber glass.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to fiber reinforced resin articles. In particularthe invention relates to methods of forming resin reinforced helicallywound composites.

2. Prior Art

The concept of reinforcing resin articles with fiberous material such asfiber glass is well known. The methods of reinforcing resin have rangedfrom the addition of short pieces of fiber of about 1/8 inch toinjection molding compositions to the utilization of woven mats of fiberin combination with resin to form laminates. Other composites have beenformed by winding resin impregnated fibers onto a mandrel. The followingreferences illustrate processes of reinforcing resins with fibers andare considered pertinent to the instant invention.

U.S. Pat. No. 3,669,638 to Wong et al. discloses a process whereinrandomly oriented glass fiber mats are formed from glass fibers whichhave been chopped and combined with a binder, preferably by spraying thebinder onto the falling fibers. Wong et al. also discloses whereincontinuous fibers are layed on a forming belt and utilized to form mats.These continuous fibers may be either sprayed with the resin after beingplaced on the mat or sprayed prior to being placed on the mat. FIGS. 6and 7 illustrate embodiments wherein continuous strands are utilized.

U.S. Pat. No. 3,873,291 to Miller illustrates a method wherein glassfilaments are continually wound onto a rotating drum and sprayed with abinder solution after being wound on the drum to form glass fiber mats.

U.S. Pat. No. 3,044,146 to Thomas et al. discloses combinations ofswirled single fiber or laterally extending continuous fibers combinedwith short chopped lengths of fiber and resin to form composite moldablearticles.

An article by Frank Ives and Louis A. Bacon titled "Chop-Hoop FilamentWinding" from the 31st Annual Technical Conference, 1976 ReinforcedPlastics/Composites Institute The Society of the Plastics Industry, Inc.Section 23-A, pages 1 through 4 discloses a method which is acombination of hoop winding and chopped strands gunning. In the methodtherein disclosed hoop winding of strands is carried out with gunning ofchopped strand and resin onto the drum surface immediately prior to thecovering of an area with the hoop strand.

All the above systems produced useful products. There remaindifficulties in the formation of high strength materials. With the aboveformation methods it is difficult to achieve good bonding of the fibersespecially glass fibers with the resin at high concentrations of glassfibers. At high concentrations of glass fibers without good wettingdelamination defects cause low strength products to result. A furtherdifficulty with the above products is that the strength of the materialis not consistent due to irregular coating of the resin and irregularpresence of the resin in some areas of the product. The method ofapplying resin to chopped fiber in a gun produces an inconsistentcoating as the gun tends to apply globs of resin and fibers rather thana continuous coat. Another difficulty with the chop-hoop method is thatthe entire resin amount must be added with the chopped fibers andtherefore adequate wetting of the wound strands does not take place.Therefore there remains a need for a high strength, high quality fiberreinforced resin composite, with improved transverse physical propertiesthat is moldable in heated press molds.

A process has been proposed in copending application Ser. No. 8,365filed Feb. 1, 1979 titled "High Strength Composite of Resin, Helicallywound Fibers and Chopped Fibers and Method of its Formation" inventorsE. P. Carley and R. H. Ackley for formation of a composite of helicallywound resin coated fibers in combination with chopped fibers. Thisproduces an excellent product. However, there is still a need for aproduct that has better penetration and delamination resistance for usein areas of high impact such as loading platforms and truck beds.Further, the chop process results in some loss of fibers as some choppedfibers are lost as they do not stick on the mandrel and fall to thefloor.

SUMMARY OF THE INVENTION

It is an object of this invention to overcome disadvantages of priorprocesses.

It is another object to form high strength resin-fiber compositearticles.

It is a further object to produce moldable high strength glass fiberreinforced composites that have improved strength in the transversedirection.

It is another object to produce a resin-glass strand composite that doesnot warp.

It is again a further object to produce resin-fiber composites with lowwaste of fiber and resin.

It is an additional object to produce resin fiber composites of highfiber content.

It is another further object to produce a composite with very goodresistance to impact.

It is another object of this invention to form composite high strengtharticles without waste.

It is again another object of this invention to produce resin-fibercomposites of uniform properties.

It is an additional further object to produce high strength resin-fibercomposites that have high resistance to delamination caused by impact.

These and other objects of the invention are accomplished generally bywinding resin wetted strands of fiber glass in a helical pattern onto adrum while applying dry swirled strands of fiber to that area of thedrum where they are immediately covered by the winding of the strands inthe helical pattern.

In a best mode of the invention the fibers are glass strands fromforming packages that are utilized in an amount such that the compositeformed has a content of about 50 parts by weight wound strands, about 25parts by weight swirled fiber glass strands and about 25 parts by weightresin matrix. The resin is applied in a carefully metered amount bypassing the strands of glass through a bath and then through a closetolerance orifice that controls resin content prior to application tothe drum in the helical winding. It is further preferred for thestrongest composite to have a helix winding angle of between about 82°degrees and 87.5° degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat schematic view in perspective of the apparatus forcarrying out the process of the invention.

FIG. 2 is a fragmentary perspective view of the apparatus showinglaydown of the continuous fiber and the relationship of the swirlapplicator and strand winder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described generally with reference to theprocesses illustrated in FIG. 1.

A creel 12 containing forming packages 14 is arranged such that thethreads from the fiber glass forming packages may be withdrawn by meansof eyelets 15 for feeding to the process. A ceramic eyelet is utilizedfor feeding each forming package from the creel. The strand end from theforming packages 14 are fed through the knock out board 25 which furtherfeeds the single package strands without twisting and with minimumabrasion to the strands. The strands are led from the knock out board 25into the strand grouping guide bar 31, and then into the bath generallyindicated by 32. The bath is formed of a container 33 having inletceramic guides 35 in guide bar 31. The strands after entering the baththrough the ceramic guides 35 are drawn under the surface of the resinbath and kept submerged during passage through the bath by rods such as36. The exit orifices 34 from the bath are regulated to close tolerancesto meter a measured predetermined amount of resin onto each of thegathered strands. The use of forming package strands that have not beenjoined prior to entry in the bath allows better wetting while the closetolerances of the exit orifices insure a carefully metered amount ofresin being adhered to the strands. The level of resin in the bath iscontrolled by a level regulating means not shown which regulates theaddition of the bath components from the source of resin generallyindicated as 72. After leaving the bath 32 the strands now coated withuncured resin are led to the winder generally indicator by 52. Thestrands are led to the traversing carriage 55 on which is mounted astrand guide plate 51 and a spacer bar 57 having eyelets withpredetermined spacing and diameter. The eyelet's diameter and spacing onthe spacer bar 57 of traversing carriage 55 are important to insure thatthe strands are not abraded by the eyelets and that the strands are atthe proper spacing such that the helical winder will lay or rest strandsof successive layers precisely in the spaces between the strands ofthose layers previously wound. The rotational speed of the drum 54 iscontrolled by selection at the winder control 53. Changing of themachine settings allows various helix angle variations.

Strands for the swirled fibers are led from the source generallyindicated at 22 comprising creel 23 having the forming packages 14 ledthrough eyelets 15. From the creel the strands are led through ceramicguides in knock out board 26 then through guide 74 to the swirled strandapplicator 56 where they are applied to the mandrel immediately beforethe resin impregnated continuous strands contact the continuous windingmandrel. The swirled strands are applied by conventional air motorchopper gun 56 that has the cutting blades removed. The strands areapplied at a rate that causes them to lie on the mandrel in swirls 77 asthey are overfed at a rate greater than the peripheral speed of thedrum. The gun is mounted on the lower portion of traversing carriage 55such that is can project the swirled strand 77 under the collimatedcontinuous strands 78. The air hose 73 supplies air to drive the gun.While the apparatus illustrated utilizes a traversing carriage androtating mandrel for the helical winding it is also within the inventionto utilize a mandrel that both rotates and moves along its axis whilewinding from a stationary source of strands.

The composites of swirled fibers and helically wound fibers result in acomposite molding sheet which is suitable for processing into structuralshapes through the use of heated matched-metal-molds and hydraulicpresses. The swirled strand helically wound composite also could beutilized with winding around an inflatable core and curing on the coremember to directly create a shaped article. The need to remove weightfrom power driven vehicles has increased and consequently the need forhigh strength, high density materials to replace metals in structuralparts for the transportation industry has also increased. The compositeof the instant invention provides the high strength, moldability andweight reduction not found in other articles.

In discussion of the process and product of the instant invention, it ishelpful that certain terms are defined. The following definitions willbe used in this specification.

Mandrel: The form around which the winding is accomplished.

Band or Ribbon: A term applied to the collimated strands as they arewound onto the mandrel.

Band or Ribbon Width: The width of the band measured perpendicular tothe band direction.

Circuit: One complete cycle of carriage motion.

Pattern: A complete pattern is formed when a band of fibers liesadjacent to a perviously wound band. If the bands become adjacent afterone cycle of the carriage, there is one circuit per pattern. If twocycles of the carriage are necessary before the band lies adjacent to aband previously wound, then there are two circuits per pattern, and soon. T:C is the ratio of "mandrel revolutions to complete a pattern" to"traversing circuits to complete a pattern."

Layer: A covering of the mandrel in both traversing directions by theribbon or band. In the case of a solid ribbon, a layer would completelycover the mandrel; while in the case of an open ribbon with spacingbetween the strands, a layer would not completely cover the mandrel asopen diamonds would be present.

Ply: A complete covering of the mandrel with no open diamonds. In thecase of a solid ribbon or band, a layer would equal a ply. An openribbon requires more than one layer to obtain a ply, and the number oflayers required depends on the spacing between the strands and thestrand width.

Crossovers: Crossovers cause an interweaving of the fiber glass strandsas they are wound onto the revolving mandrel; interweaving is increasedwith an increased number of crossovers. Crossovers can be achieved bywinding a ribbon having spacing between the collimated fiber glassstrands. Crossovers of solid ribbons are achieved by increasing thenumber of circuits required to complete a pattern, that is, byincreasing C in the T:C ratio.

Helix Angle: α--The included acute angle created by the intersection ofthe band on the body of the mandrel with a line on the body of themandrel parallel to the longitudinal axis of the mandrel.

Winding Angle: β--The included acute angle created by the intersectionof the band on the body of the mandrel with a line on the body of themandrel perpendicular to the longitudinal axis of the mandrel.

The instant invention allows utilization of a variety of resins andfibers to achieve differing product properties. Among the variableswhich influence the process and composite of the instant invention arethe fiber content of the composite, the helix angle, winding angle, theratio of continuous strand to swirled strand to resin, the resincomposition and the spacing between strands.

Any fiber may be used in the instant invention which results in acomposite of high strength and possesses the integrity necessary for thewinding process. Typical of fiber utilized in the invention arepolyimide, polyester fibers, polyamide fibers, natural fibers and metalfibers. Suitable for the invention are polyaramid fibers (KEVLAR®DUPONT). Preferred fibers for the instant invention are glass fiberstrands and carbon strands as these materials result in high strengthproperties and are suitable for swirling or winding on the mandrel ofthe invention to form resin fiber composites. An optimum material hasbeen found to be glass fibers from forming packages as such fiberspossess superior wetting properties, do not filamentize readily andprovide good bonding with the resin.

The resin utilized in the instant process and composite may be anymaterial that provides the necessary bonding and strength for thecomposite article formed. Among typical resins are polyolefins,polyaramids, novalacs and polystyrenes. Suitable resins for the instantprocess are vinyl esters epoxy resins, polyurethanes and polyesters.Typical of heat curing polyester resins that may be employed in theinvention are those disclosed in U.S. Pat. Nos. 3,772,241 to Kroekel;3,701,748 to Kroekel and U.S. Pat. No. 3,840,618 to DaFano. Preferredresin materials are thermally cured polyester resins as these materialsprovide a high strength composite and give reasonable shelf life to thecomposite prior to their curing during the heat and pressure formationof the composite. When forming the preferred molding compound a resinwhich does not degrade significantly during storage and cures during theheat and pressure of forming is necessary.

The ratio of continuous helically wound strand, swirled fibers and resinmatrix may be adjusted to any combination which results in an acceptablemoldable article. The amount of continuous strand in the finishedarticle may suitably be between about 79 and about 20 percent by weight.A preferred amount of continuous strand in the finished article isbetween about 45 and about 60 percent by weight of the continuous strandfor the strongest composite article. The amount of swirled fibers in thefinished composite may suitably be between about 1 and 60 percent byweight. A preferred amount of swirled fibers is between about 20 and 40percent by weight of the composite to give good strength transverse tothe direction of continuous strand winding. The range of resin in thecomposite may be between about 50 and about 15 percent by weight. Apreferred amount of resin is between about 20 and about 35 percent byweight of the finished composite for proper wetting and optimizedphysical properties.

The helix angle of winding on the mandrel may be selected to give thedesired properties to the composite article and to minimize waste at theends of the mandrel. Typically the helix angle may be as small as 45°,or as large as 89.9°. A suitable angle is between about 71° degrees and89.89° degrees for a composite article with minimum waste. A preferredhelix angle is between about 82.5° and about 87.5° for a very strongcomposite article with good molding characteristics. The optimum helixangle has been found to be about 85 degrees for optimum molding ofcomplex shapes at optimum strength. An optimum composite has been foundto be one comprised of about 50 percent by weight wound continuousstrand, 25 percent by weight swirled fibers and 25 percent by weightresin matrix wound at a helical angle of about 85° degrees to give highstrength in the direction of primary reinforcement and satisfactorystrength transverse to primary reinforcement.

The method of continuous strand impregnation may be any method whichresults in a close control of the resin pickup of continuous woundstrand such that uniform application and wetting of the continuousstrand takes place. A preferred method is that illustrated in thedrawing wherein the continuous strands for winding are passed through aresin bath and then drawn through close tolerance orifices. Thepreferred orifices are wire drawing dies. This method allows regulationof the resin content of the fiber to a plus or minus 2 percent of adesired resin to reinforcement weight and more typically plus or minus 1percent of the desired amount of resin. The preferred glass strand fromforming packages is drawn such that between 1 and 15 ends pass througheach orifice. The preferred glass strand is K-37.5 from forming packageswith passing five of these strands through each orifice of the bath. Thestrands may be coated by other methods if the necessary accuracy ofresin coating can be maintained or if the particular product beingformed does not require the uniform coating of the preferred materialsof the invention. Typical of other methods of coating are passingthrough a bath followed by squeegee or roll removal of excess coatingand spraying the coating onto the fibers. The viscosity of the resin ispreferably between 400 and 1200 centipose for good pickup from the bathonto the forming package fibers. The helical winding may be continued toform any number of layers desired. Preferred are three complete plys ofwound material. As this creates a composite that has high strength andmolds to a thickness of about one eighth inch which is suitable for bodyparts of cars and trucks. For thicker parts several 3 ply sheets may becombined in the molding process.

The swirled fibers may be applied by any conventional device that isable to project it onto the mandrel in a stream narrow enough to beconcentrated under the continuous strands as they are applied to themandrel. The preferred fibers for swirl application are from K-37.5forming packages. They maintain their strand integrity when swirled andmost important they wet well with the resin carried by the continuousstrands. The diameter of the swirls on the mandrel may be varied at thesame glass content by using more strands at a slower application rate orfewer strands at faster application.

The winder for producing helical winding may be any commercial winder. AMcClean-Anderson W-2 filament winder operated at about 500 feet perminute mandrel surface speed with a mandrel diameter of about 35 incheshas been found to be suitable. However, other winders are commerciallyavailable and may be utilized. The winders incorporate various gearsettings or electrical controls which may be regulated to produce thedesired helix angles and desired laydown continuous patterns. Spacingbetween strands is controlled by the spacer bar mounted on thetraversing carriage. The distance between the continuous strands iscarefully regulated by the center spacing of the spacer bar eyelets. Theformation of three layers is preferably carried out to produce a singleply sheet. By fine tuning of the helix angle it is preferred toprecisely nest the continuous strands of the second and third layersinto the continuous strand spacings of the first layer. This results inas thin as possible composite having no open diamonds and yet havingmany stress transfering crossovers. In order to achieve this desirednesting of the continuous strands it is necessary that the spacingbetween the ribbons be equal to the spacing between the continuousstrands. The methods and apparatus for helical winding of continuousstrands are known in the art and do not by themselves form a novelfeature of the invention. However, the preferred method of the instantinvention wherein the successive layers are wound such that the strandsof the second layer are precisely nested between the strands of thefirst layer and the third layer strands are precisely nested betweenthose of the second and first layers has not been practiced in the artand has been found to give maximum strength in the instant process. Thenesting of strands results in the maximum number of crossovers betweenthe strands. Such crossovers increase the strength of the article formedin the instant invention.

The following example illustrates a preferred embodiment of theinvention. Parts and percentages are by weight unless otherwiseindicated.

EXAMPLE I

A creel of 60 forming packages containing K-37.5 fiber glass continuousstrand is arranged to be drawn such that 50 of the continuous strandsare drawn through each of 12 orifices and into a bath for coating with aresin. The bath contains PPG 50335 heat curing isophthalic polyesterresin. The continuous strands are withdrawn from the bath through closetolerance orifices selected such that they pick up an amount of resincorresponding to about 50% percent of the strand weight entering thebath. A group of 3 forming packages is arranged on a creel and drawn toa chopper gun that has been modified by removal of the chopper blades.The feed by the modified chopper is a rate that corresponds to half theweight of glass fiber drawn through the bath and is projected in swirlsonto the mandrel. The close tolerance orifice diameter is about 0.037inches and comprises a wire die. The winder is a McClean-Anderson W-2winder rotating a mandrel about 31 inches in diameter at a peripheralspeed of about 300 fpm. The mandrel is covered with a sheet of polyvinylchloride plastic film to act as a release and a storage covering. Thewinder is programmed to produce a sheet of about 48 inches in width onthe mandrel. The traversing mechanism of the winder is fitted with aspacer bar having a space on center between the continuous strands beingapplied to the mandrel of about 0.26 inches. This results in a spacingbetween the strands of about 0.16 inches. The winder is programmed toleave the spacing between the ribbons of about 0.16 inches. The resinbath temperature is maintained at between about 80° degrees and about85° degrees F. The winder is operated at a helix angle of about 84.76°degrees. The spacer bar located on the traversing mechanism is mountedin such a position that the continuous strands go with little deviationfrom the spacer bar directly to the top of the mandrel. The modifiedchopping gun directs the swirled fibers to a point on the mandrelimmediately to be covered by the continuous strands as they are wound onto the mandrel. They swirl in ringlets between about 0.5 and about 1.5inches in diameter. A first layer of continuous strands are wound ontothe mandrel then as the second layer starts the modified chopper gun isstarted to begin applying swirled fiber glass. The winder requires threelayers to form one ply. After the formation of the eighth layer, theswirled strand is discontinued and the ninth layer which is the finallayer of the third ply is applied without the chopper in operation. Thethree plys of composite are then covered with plastic film. Thecomposite sheet is slit and removed from the mandrel. One foot squaresections of the composite are molded at about 500 psi for 3 minutes.These samples are then tested and found to have the following propertiesin the direction perpendicular to the winding direction: tensilestrength about 9 to 11 thousand psi, flex strength about 19 to 21thousand psi and flex modulus about 1.1 to 1.3×10⁵ the measurements inthe direction parallel to the winding direction are tensile strengthabout 80,000 psi, flex strength about 135,000 psi and flex modulus about5.75-6.0×10⁶ psi. These strengths in the direction perpendicular towinding are very good. Additionally the composite has a good resistanceto delamination upon impact. The overall composite comprises 50 partswound strand, 25 parts swirled strand and 25 parts resin. The impactresistance is such that delamination does not occur when a sample issubjected to a Drop Dart Test. In the test a 10 lb. steel dart with 1"radius point is dropped from a height of 6 ft. The result is a slightdented surface at impact point and very light resin cracking on reverseside.

EXAMPLE II Control

As a control, the process of Example I is repeated except that theswirled fiber is not utilized. The material without the swirled strandmaterial fiber is found to have a tensile strength perpendicular to thewinding of about 2,000 psi. This is only about 1/5 the strength that isgained in the instant invention by the use of the swirled fiber incombination with the helical winding.

EXAMPLE III Control

As a control the process of Example I of the above-referenced Carley andAckley copending application is repeated. A sample of the material istested by the impact test of Example I and the impacted surface isdented and shows resin cracks. The reverse side of the impact isfractured and shows a degree of laminate delamination. This illustratesthe unexpected impact resistance advantage of the instant material.

Although this invention has been described with reference to theparticularly preferred embodiments those skilled in the art ofreinforced plastics will recognize that variation may be made in thepractice of this invention by departing from the concepts disclosedhere. For instance, the composite formed by the method of the inventioncould utilize any combination of wound or swirled continuous glassstrands and wound or swirled graphite or carbon strands. Further theprocess of the invention could be practiced with thermoplastic resinssuch as polypropylene to form low cost, low temperature but highstrength products. In a further modification of the invention it ispossible to change the process of the invention by modifying the numberof winding layers under which swirled fibers are placed. It may bedesirable in some instances to not place swirled strand under each layerexcept the surface layer as in the preferred embodiment. In someinstances the surface properties may be improved by placing all theswirled strand in the middle five or six layers of wound continuousstrand. Swirled pigmented strands on, at or near the surface could beutilized for improved visual effects. Accordingly, this disclosure isintended to be illustrative rather than limiting and the inventioncorresponds to the claims accompanying this disclosure.

I claim:
 1. A method of forming a heat curable continuous glass fiberreinforced composite sheet suitable for molding into a shaped partcomprising the steps of,(a) Passing a plurality of continuous glassstrands through a liquid bath of heat curable resin to thoroughly wetsaid strands with resin, (b) Removing the resin wetted strands from saidbath, (c) Passing each of said strands removed in (b) through a closetolerance orifice to remove excess resin and to provide on each strand adesired weight quantity of resin basis the weight of the strand, (d)Removing the strands from said orifices, (e) Passing each of the strandsthrough an eyelet in a spacer bar to align the strands in a side by siderelationship at precisely spaced distances from each other. (f) Windingthe strands on a rotating mandrel at a helix angle of between 45 to 89.9degrees while traversing the spacer bar across the long axis of saidmandrel to thereby provide on the surface of said mandrel as it rotatesa series of bands of resin coated continuous strands, (g) Continuing towind strand in (f) until a layer of strand has been deposited on saidmandrel, (h) When the layer of step (g) is provided introducing onto thesurface of said mandrel a second group of continuous strands at a rateof speed higher than the peripheral speed of said rotating mandrel tothereby deposit said strands in a swirl pattern and at a point close tobut below the point of contact of said helically wound strand to therebytrap said swirled strand under said resin coated strand and to wet saidswirl strands with resin, (i) Continuing to wind said resin-coatedstrand and said swirled strands until the desired plies have beenapplied, (j) Discontinuing winding when step (i) has been completed andcutting and removing from the mandrel the resulting composite sheet. 2.The method of claim 1 wherein the helix angle in step (f) is between 71°and 89.9°.
 3. The method of claim 1 wherein the helix angle in step (f)is between 82.5° and 87.5°.
 4. The method of claim 1 wherein the helixangle in step (f) is 85°.
 5. The method of claim 1 wherein the totalcontinuous glass fiber reinforcement introduced in steps (f), (h), and(i) in forming the composite sheet is 25 to 79 percent by weight of thecomposite.
 6. The method of claim 5 wherein said swirled strandscomprise 20 to 40 percent by weight of said composite.
 7. The method ofclaim 5 wherein said swirled strands comprise 25 percent, said woundstrand 50 percent and said resin 25 percent of said composite by weight.